dog ( labradore retriever) with cyst

we had recently found a lump under our dogs arm ( near the arm pit) , and it is like a sac of fluid . could this be a cyst?

Hi,

You are right that is could be cyst. But there are lost of other things that could feel like just a cyst. Tumors often start off appearing like this so it is important that anytime you see a cyst or mass on your dog you have your vet examine it.